Variable pitch rotor blade with double flexible retention elements

ABSTRACT

A propulsive thrust device for an engine includes a rotor blade and a hub assembly on which the rotor blade is mounted. The rotor blade comprises an airfoil and at least two support members. A propeller thrust device includes a rotor blade, a central hub at which the rotor blade centrifugal load is supported, and an outer hub supporting a control mechanism mechanically connected to the rotor blade and controllable to vary the pitch of the rotor blade on the central hub. A rotor blade for an aircraft engine or in a separate ducted fan housing driven by a powered shaft or gearbox output shaft includes an airfoil and first and second support members attached to the airfoil. An extended arm or portion of the structure at the root of the airfoil of each blade is attached to a controllable mechanism that can vary the pitch of all blades simultaneously.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.11/349,817, filed on Feb. 7, 2006, which claims the benefits of U.S.Provisional Patent Application Ser. No. 60/651,089, filed on Feb. 7,2005, the contents of both applications being incorporated herein byreference in their entireties.

TECHNICAL FIELD

This invention relates in general to rotor blades and, moreparticularly, to rotor blades for propulsive thrust devices in aircraftengines in which the rotor blades can be varied in pitch to controlthrust-producing and/or power-absorbing capacities of such devices.

BACKGROUND OF THE INVENTION

Standard configurations of rotor blades typically used in aircraftrotary propulsion systems that allow variable pitch operation usuallyinclude a root attachment mechanism such as a ball/roller bearing and/orflex member, both of which allow pitch change of the blade withrelatively low friction between components. To impart the necessarystructural integrity to such mechanisms (e.g., to accommodate thesubstantial centrifugal forces exerted on the mechanisms duringoperation), they are often fabricated in such a way so as to beextremely heavy. A further complication is that substantial centrifugalloads on the plate-like structures of the blades themselves also producesignificant twisting or turning forces that pitch control systems mustovercome. These forces tend to turn the blade towards an undesirableflat pitch position. In the event that a malfunction of the pitchcontrol system occurs, the forces acting on the blades could turn theblades to the flat pitch position, reducing rotor rotational resistance,thereby resulting in rotor overspeed conditions and potential bladeloss.

As stated above, the turning force that acts on a rotor blade during itsnormal operation is substantial. In propulsion technology as it appliesto fans and propellers, this force is referred to as the total twistingmoment (TTM). The TTM is the net sum of three basic forces, viz., thecentrifugal twisting moment (CTM), the aerodynamic twisting moment(ATM), and the frictional twisting moment (FTM). The CTM, which istypically the most substantial of the forces, originates from anon-symmetrical mass distribution of an airfoil of a rotor blade about apitch change axis of the airfoil. In other words, in an oblong airfoilhaving a non-circular, non-symmetrical cross section, the mass about thepitch change axis is not evenly distributed, and centrifugal forcesoriginating from the rotor's axis of revolution and acting on elementsof the airfoil cause inertial twisting forces. The ATM is caused whenthe effective center of pressure on each section of an airfoil of arotor blade is forward or aft of the pitch change axis. The FTM resiststurning motion and develops in retention bearings that support the rotorblade due to high centrifugal loads acting on the bearings. In theoperation of a rotor blade in which all three forces are taken intoaccount, the CTM acts to turn a rotor blade toward low pitch, butbecause the aerodynamic center of pressure of an airfoil is usuallyforward of the pitch change axis, the ATM opposes and counters the CTMto turn the rotor blade toward an increased blade pitch. The FTM, whichis caused by friction, opposes blade pitch change in either direction.

The forces of the pitch control system required to overcome the forcesacting on the rotor blade during its operation can be appreciable. WithTTM being dominated by CTM, the pitch control system of a typical rotorblade device exerts a torsional load in the direction of increased pitchto hold the blade pitch constant. The system must also exert anadditional force to overcome the FTM in order to increase the bladepitch. However, if there is a malfunction and/or loss of control of thepitch control system (e.g., due to loss of engine power), a rotor bladewill naturally turn toward lower pitch. Because low pitch results inless rotational resistance for the engine, the situation can result inan undesirable overspeed of the rotor and engine. In extreme conditionsin variable pitch systems with no low pitch stop, the TTM can turn theblades to low pitch, and rotor thrust can suddenly switch to a high dragforce that can cause possible loss of aircraft control and/or result inrotor overspeed. Rotor overspeed is more likely if the rotor is drivenby a turbine engine rather than a piston engine, especially if thatsegment of the turbine that powers the rotor is separate from otherturbine components. This turbine is referred to as a “free” turbine(i.e., there is no revolution limiting capability). In a single engineaircraft, increased drag can limit glide distance for an unplannedlanding, while in a twin engine configuration, the asymmetric drag ofone disabled propulsor can hinder the ability of the pilot to controlthe aircraft.

To prevent undesirable pitch tendencies, counterweights have been addedto the sides of rotor blades and at or proximate the root ends of therotor blades. Such weights are typically of sufficient mass to create anet TTM that will be able to overcome all inherent rotor blade turningforces and drive the rotor blades toward higher pitch (or at leastmaintain the pitch setting to prevent movement toward lower pitch).These weights have also been known to be substantial in mass, therebyadding unsprung weight to the rotor blades and further loading thebearings associated with the rotor hub and blade retention mechanisms.Also, these weights often have associated retention mechanisms or otherdevices that may be prone to failure under normal operating conditionsdue to the mechanical stresses encountered. If a failure is experienced,the high energy of the released mass may result in impact damage as wellas high rotor unbalance conditions. Other pitch control systemstypically employ auxiliary electric pumps that provide backup pressurefor a hydraulic system, linear ACME thread harmonic drives, and/orlatching devices that hold position. In at least some of these systems,if the pitch of the rotor blades is maintained in a less than optimumposition for gliding (in an aircraft having a single engineconfiguration) or for compromised operation (in an aircraft having atwin engine configuration), increased drag forces may be generated whichinhibit the ability of an operator to properly manage the system.

Based on the foregoing, what is needed is a device for efficiently andcontrollably varying the pitch of a rotor blade in an aircraftpropulsion device. Also, what is needed is a rotor blade for an aircraftpropulsion device that is capable of being efficiently and controllablyvaried.

SUMMARY OF THE INVENTION

According to one aspect, the present invention resides in a propulsivethrust device for an engine. Propulsive thrust devices that are withinthe scope of the present invention include, but are not limited to, fansand turbo-fans for use in jet aircraft engines, ducted fans driven byshafts or gearboxes, propellers for use with rotary piston aircraftengines, rotors or fans for use in helicopters or other vertical/shorttake-off and landing aircraft, and the like. Such devices include arotor blade and a hub assembly on which the rotor blade is mounted. Therotor blade comprises an airfoil, a first support member depending froma forward portion of the airfoil, and a second support member dependingfrom an aft portion of the airfoil. The hub assembly comprises either asingle spool to which both support members are attached or a first spoolon which the first support member is attached and a second spool onwhich the second support member is attached. If two spools are utilized,the second spool is coaxially aligned with the first spool. A collectorring is coaxially aligned with and rotatable relative to the hub and maybe supported with a bearing mechanism attached thereto. The rotor bladehas a platform at the root of the airfoil that includes a lever armextended some distance from the pivot center and mechanically connectedto the collector ring. This arm is positionable relative to the hub viarotation of the collector ring to allow the pitch of the rotor blade tobe varied. The fan assembly itself is rotatable about a centerline axisextending longitudinally therethrough to produce thrust as a propulsionsystem.

According to a second aspect, the present invention resides in apropeller thrust device that includes a rotor blade, a central hub atwhich the rotor blade centrifugal load is supported, and an outer hubsupporting a control mechanism mechanically connected to the rotor bladeand controllable to vary the pitch of the rotor blade on the centralhub. The rotor blade comprises an airfoil having a hollow root, a firstsupport member flexibly attached to a forward portion of the airfoil anddepending through the hollow root, and a second support member flexiblyattached to an aft surface of the airfoil and also depending through thehollow root. The rotor blade is attached to the central hub at the firstand second support members and is guided for pitch angle turning by abushing or sealed rotary ball or roller bearing in a mating hole throughthe arm of the outer hub.

In a third aspect, the present invention resides in a rotor blade for anaircraft engine or in a separate ducted fan housing driven by a poweredshaft or gearbox output shaft. The rotor blade includes an airfoil andfirst and second support members attached to the airfoil. Both the firstand second support members are attachable to a rotatable hub and movablerelative to the rotatable hub to allow pitch of the rotor blade to bevaried. An extended arm or portion of the structure and/or flow path atthe root of the airfoil of each blade is attached to a controllablemechanism that can vary the pitch of all blades simultaneously.

In any of the disclosed embodiments, the pitch of the rotor blade may bevaried controllably, or the pitch may be allowed to change in responseto operational conditions of an aircraft in which the rotor blade isutilized.

One advantage of the present invention is that the thrust-producingand/or power-absorbing capacity of a propulsive device is more easilycontrolled because dual support of the rotor blade helps balance highCTM forces. The reduction derives from alignment of the blade masselements from the forward and aft portions of the airfoil with eachrespective support member, and/or the positioning of the attachmentpoints of these members to create a desirable restoring, twisting forcewhen centrifugal load is applied. In general, these support members tendto follow an extension of the natural cumulative twist built into eachairfoil required to align airfoil sections with local airflow vectorsalong the length of the blade. Changes in rotor operating conditions(e.g., variations in air velocity entering the rotor, the level of powerapplied to the rotor, and the like) can be compensated for or controlledto limit drastic responses of the device. For example, a rotorpropelling an aircraft can experience or require significant changes invelocity and operating power between static thrust operations,take-offs, climbs, cruise conditions, and descent conditions. By varyingthe pitch of the rotor blades accordingly, efficiency (e.g., fueleconomy) and responsiveness of the device can be realized.

A primary advantage for propellers is that high blade centrifugal forcescan be efficiently supported by a much smaller, compact, central innerhub. The outer hub is thus lightly loaded, supporting mainly the bladebending and thrust loads while providing a pivot center about which theblade can turn when changes in pitch are commanded by the pitch controlsystem. As such the outer hub can be constructed as a thin, lightweightstructure of various low cost materials.

Another advantage for both propellers and fan applications is that theneed for a counterweight on each blade as a pitch control backup systemis eliminated. Without the counterweights, additional loading of therotor hub and bearings is eliminated, thereby reducing the size andamount of wear to the device. Furthermore, without a counterweight, therisk of failure of the associated retention mechanisms is eliminated,which in turn removes the possibility of impact damage resultingtherefrom as well as rotor unbalance conditions.

Still another advantage for both propellers and fans is that astructurally efficient means of blade attachment is realized. Bladeattachment using this means is especially well-suited to the design andfabrication of thin, efficient, lightweight, composite rotor blades.

Still another advantage for fan designs is derived from the calculatedfrangibility of a post and/or mating receptacle on which the rotor bladepivots. By being calculated to fail under excessive loading from bladeimpact with foreign objects (e.g., from the development of abnormallylarge loads such as from the ingestion of birds, runway debris, or otherforeign objects), the blade is allowed to swing more freely withoutfracture of the support members. Thus blade loss and extreme unbalanceconditions may be mitigated.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective cutaway view of a fan, of the present invention,in which a rotor blade is mounted on a hub and is pivotable on the hubvia a rotatable collector ring to provide variable pitch to the rotorblade.

FIG. 2 is a perspective view of a rotor blade, of the present invention,mounted on the hub, of the present invention.

FIG. 3 is a section view of the rotor blade of FIG. 2 mounted on thehub.

FIG. 4 is a perspective cutaway view of an alternate embodiment of afan, of the present invention, in which a rotor blade is mounted on anindependently rotatable hub assembly capable of providing variable pitchto the rotor blade.

FIG. 5 is a section view of the independently rotatable hub assembly ofFIG. 4.

FIG. 6 is a perspective view of a rotor blade, of the present invention.

FIG. 7 is a cutaway view of a propeller application in which a rotorblade is mounted on a central hub within an outer hub having a pitchcontrol mechanism capable of providing variable pitch to the rotorblade, of the present invention.

FIG. 8 is a perspective cutaway view of the propeller applicationshowing the mounting of the rotor blades on the hubs.

FIG. 9 is a perspective view of a portion of the airfoil pressuresurface and root attachment members of a rotor blade of the propellerapplication of FIG. 7.

FIG. 10 is a perspective cutaway view of a portion of the suctionsurface and root attachment members of a rotor blade of the propellerapplication of FIG. 7.

FIG. 11 is a perspective view of a pin used to preload a rotor blade ofthe propeller application of FIG. 7.

FIG. 12 is a perspective cutaway view of the pin of FIG. 11.

FIG. 13 is a perspective view of a rod of the pin of FIG. 11.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention utilizes a configuration of associatedindependently controllable support members to vary the positions ofrotor blades. Although only two support members are shown for each rotorblade, it should be understood that any number of support members may beused to control a rotor blade. In propulsive thrust devices, thepositions of the rotor blades are variable primarily to optimize theangular orientation of part or all of the airfoil surface relative tolocal air flow direction(s) along the length of a rotor blade developingpropulsive thrust. Because the air flow direction changes with operatingcondition, adjustment of blade pitch angle can provide significantincreases in propulsive efficiency resulting in greater fuel economy.Although the propulsive thrust devices referred to herein are referredto as aircraft engines, it should be understood that any type of devicehaving a rotating blade is within the scope of the present invention.

Referring to FIG. 1, one exemplary embodiment of a fan for an aircraftengine is shown generally at 10. The fan 10 is preferably for a turbofanengine, although the present invention is not limited in this regard andother types of airfoil devices (e.g., propellers, helicopter rotors, andthe like) can be easily adapted to the principles described herein andare within the scope of this disclosure. Fan 10 comprises a hub 12 and aplurality of rotor blades 14 mounted on the hub. The hub 12 issymmetrically mounted on a fan shaft 16 that is coincident with a hubcenterline axis 18 about which the fan rotates. The rotor blades 14 areeach attached to the hub assembly 12 via two members 22. When mounted,the rotor blades 14 each extend radially outwardly from the hub 12 alonga rotor blade axis 26.

The root end of each blade's airfoil is enveloped with a contouredshape, referred to as a platform that describes and/or provides closureor sealing of the inner flow path of the air being compressed oraccelerated by the fan. This may consist of one piece which is integralwith the blade or two separate pieces that can be clamped around thejunction of the root support members to the blade's airfoil. Thejunction between the platform and the blade proper may be accomplishedwith a potted semi-flexible material such as silicone rubber and/or apolyurethane compound to allow flexure at the junction without loss ofjoint integrity. By extending sufficiently outward from both sides ofeach blade, these platforms overlap one another to form a seal for theinner flow path of the air between blades. The overlapping edges ofthese platforms can be made thin and flexible to allow limited turningof each blade, yet be preloaded enough against each other as to alwaysstay in contact. In so doing, these platforms can be made to also dampenblade vibration. Also, the central region of the platform can be moldedor shaped into a receptacle for receiving the pivot post or bushing orbearing which defines the blade's pitch change axis. Furthermore, theforward end of this platform can be extended to provide a mechanicaladvantage in the form of a lever arm with a small slot for controllingpitch of the blade. This slot in each rotor blade 14 mates with a rollerbushing on a collector ring 17, which is coaxially aligned with andadjacent the hub 12. Although the platform lever arm and collector ring17 are shown positioned forward of the hub 12, the present invention isnot limited in this regard as the lever and collector ring may bepositioned aft of the hub, or dual levers and rings can be positionedboth forward and aft of the hub.

Central bearing posts 30 are positioned adjacent the hub 12, each postoptionally providing support to its respective rotor blade 14intermediate the two members 22 and allowing for the pivotal movement ofthe rotor blade about the rotor blade axis 26. The posts 30 may bethreaded to facilitate the preloading of the rotor blades 14 and anyassociated bearing structure in an outwardly radial direction duringassembly of the fan 10. Additionally, the posts 30 may be sufficientlystrong to support normal operating loads but purposely fabricated to besufficiently frangible to fail under excessive loading. Additionally oralternatively, the mating receptacle at the center region of the bladeroot platform can be made frangible.

The collector ring 17 is supported on the hub 12 by a bearing 19 and mayhave a rib 21 that projects radially outwardly from an outer surface ofthe ring. Roller bearings attached to the ring mate with slots in bladeplatform lever arms at the front of each rotor blade 14. Slots in eachrotor blade 14 lever arm interface with rollers on the rib 21 (e.g., atthe lever arm 38). Any suitable mechanism may be utilized to rotate thecollector ring 17 to vary the pitch of the rotor blade 14. Preferably,the collector ring 17 is rotated via a harmonic drive device, althoughother devices are within the scope of the invention. During an operationin which the pitch is varied, the rotation of the collector ring 17 issufficient to impart a total turning motion of up to 10 degrees or morein either direction to the platform and airfoil portions of the blade.

To accomplish this rotation, the blade support members are constructedof multiple strands of high strength materials such as carbon, glass,Kevlar, and /or metallic fibers. These fibers are preferablysufficiently strong in tension to support high blade centrifugal forces,yet able to be molded in low modulus resins or compounds to allowsufficient rotational deflection in a short length to provide the pitchchange motion preferred. Also, many new materials may become availablein the future that will allow such motion and may be substituted forthese fibrous supports without departing from the scope of theinvention.

Referring now to FIGS. 2 and 3, the rotor blade 14 is mounted on the hub12. The hub 12 includes a forward spool 40 and an aft spool 42, bothbeing coaxially aligned on the centerline axis 18. The forward spool 40and the aft spool 42 are preferably cast, forged, or connected so as todefine a unitary member. The present invention is not limited in thisregard, however, as the forward spool 40 and the aft spool 42 may bedistally located from and cooperative with each other. Both the forwardspool 40 and the aft spool 42 are fabricated of any suitable materialcapable of imparting the necessary structural integrity to the hub 12.Exemplary materials from which the spools may be fabricated include, butare not limited to titanium, titanium alloy, carbon fiber, and the like.Preferably, the walls of the spools are titanium with carbon fiberwindings to provide hoop strength.

Bars or rods 44 extend from opposing facing surfaces 48 of the endportions of each spool to provide surfaces at which the support members22 of the rotor blade 14 can be attached. Preferably, the supportmembers 22 include holes through which the rods 44 extend, although thepresent invention is not limited in this regard as the support membersmay be attached directly to the rods. The rods 44 extend longitudinallyalong the length of each spool at an angle relative to the hubcenterline axis 18.

The rotor blade 14 may also be at least partially supported andpositioned by the post 30 that extends radially outwardly from a bladepivot support 54 that is positioned over the hub 12 and along the rotorblade axis 26 of the rotor blade. The blade pivot support 54 rotateswith the hub 12. One post 30 is associated with each rotor blade 14 toprovide pivotal movement and thereby variable pitch to the rotor blade.A bearing or bushing 56 is mounted at the point at which the post 30extends into the rotor blade 14 or mating receptacle in the centralportion of the blade platform to reduce the friction generated byrotating the rotor blade on the post to vary the pitch. In someembodiments, the post 30 and/or platform receptacle may be sufficientlystrong to support normal operating loads but purposely fabricated to besufficiently frangible to fail under excessive loading.

When the hub 12 is installed into an engine, the forward spool 40 andthe aft spool 42 are rotatable together via the fan shaft. The rotationof the collector ring 17 interfacing with the platform lever arm 38causes the flexing of the support members 22 and the pivotal movement ofthe rotor blade 14 about the rotor blade axis 26, which varies the pitchof the rotor blade.

Referring now to FIG. 4, one alternate embodiment of a fan is showngenerally at 110. The fan 110, which may be utilized for any type ofaircraft, comprises a hub assembly 112 and a plurality of rotor blades14 mounted thereon. The hub assembly 112 is symmetrically mounted on afan shaft 116 that is coincident with a hub centerline axis 118 aboutwhich the hub assembly rotates. The rotor blades 14 are each attached tothe hub assembly 112 via two members 22. As in the previously disclosedembodiment, the rotor blades 14 each extend radially outwardly from thehub assembly 112 along their respective rotor blade axes 26. Centralbearing posts 130 are positioned adjacent the hub assembly 112, eachpost optionally providing support to its respective rotor blade 14intermediate the two members 22 and allowing for the pivotal movement ofthe rotor blade about the rotor blade axis 26.

Referring now to FIG. 5, the hub assembly 112 comprises twoindependently rotatable coaxially aligned spools, viz., a forward spool140 and an aft spool 142, that are rotatable on the fan shaft 116. Abearing 155 separates the forward spool 140 from the aft spool 142,although the present invention is not limited in this regard as the twospools may be distally located from each other. Rods 144 extend betweenopposing facing surfaces 148 of each spool to provide attachment pointsfor the support members.

Referring to FIGS. 4 and 5, when the hub assembly 112 is installed intoan engine, the forward spool 140 and the aft spool 142 are rotatabletogether via the fan shaft 116. The independent rotation of the forwardspool 140 and the aft spool 142 may be effected by gearing (not shown)operably associated with each spool and the fan shaft 116, although thepresent invention is not limited in this regard and other means ofindependently causing relative rotation of the spools are within thescope of the present invention. In any embodiment, the independentrotational positioning of the forward spool 140 relative to the aftspool 142 causes the pivotal movement of the rotor blade 14 about therotor blade axis 26, which varies the pitch of the rotor blade.

Referring now to FIG. 6, one exemplary embodiment of the rotor blade 14of the present invention for use with the embodiments described hereinincludes an airfoil portion 32 and a root portion 34. The airfoilportion 32 can be solid, semi-solid, or hollow and of any suitableconfiguration and material. Preferably, the airfoil portion 32 is hollowor this hollow portion may be filled with a suitable lightweightmaterial such as foam or honeycomb, and fabricated from a thin,lightweight, composite material that facilitates an efficient operationof a fan in which the rotor blade 14 is installed. The airfoil portion32 is attached to the root portion 34 at an upper surface of a platform36 of the root portion. The platform lever arm 38 extends from theplatform 36 to provide a point at which the rotor blade 14 can interfacewith roller bearings on the collector ring or other surface to controlpitch as well as to perhaps provide additional support for the rotorblade.

In any embodiment, the two support members 22 extend from a lowersurface of the platform 36 and are of sufficient length and inherentflexibility to permit a desired amount of angular rotation of the rotorblade 14 relative to the hub assembly. The support members 22 may bestraps, tenons, torque tubes, cables, tangs, links, or linkage members.The points at which the support members 22 are attached to the lowersurface of the platform 36 are selected to allow the rotor blade 14 toperform optimally under adverse conditions, for example, by allowing therotor blade to achieve a desired pitch angle setting for a givenoperating condition. The selection of the attachment points is such thatthe total twisting moment, which is affected by high centrifugal tensionloads, acts upon the rotor blade 14 via the two support members 22 tomaintain the balance of the rotor blade or to cause it to deflect orotherwise move to a more desirable angular setting in the event of aloss of pitch control or loss of power. These points of attachment aswell as the desired angular settings are determined by suitable analysismethods (e.g., computer modeling) and verified by test procedures.

One exemplary embodiment of a propeller application for a rotor blade214 of the present invention is shown in FIGS. 7-10. Such a rotor blade214 is especially suited for propeller applications (shown at 210 inFIG. 8), which typically involve blade pitch angle ranges that aresubstantially greater than those for fan applications. In the propeller210 or similar propeller applications such as helicopter main rotors ortail rotors, the rotor blade 214 includes an airfoil portion 232 havinga hollow root to provide adequate internal space for longer supportmembers 222.

Referring now to FIG. 8, the rotor blade 214 is mounted in a compactcentral hub 212 using pins 300 that extend through the central hubparallel or angled to a centerline axis 218. The compact central hub 212supports the large centrifugal loads generated by the rotor blades 214.An outer hub 225 is positioned around the central hub 212. Because theouter hub 225 does not need to support large centrifugal forces, it maybe fabricated thin from any suitable lightweight material including, butnot limited to, aluminum, aluminum alloys, carbon fiber compositematerials, combinations of the foregoing, and the like. A sealed bearing224 with rolling elements (e.g., balls or rollers) reduces frictionbetween the root of the airfoil portion 232 and each arm 228 of theouter hub 225. The sealed bearing is in compression because the supportmembers of the blade are pre-tensioned at assembly to pre-dispose theblade to turn to a desired low pitch angle to prevent overspeed underall loading conditions, even when loss of pitch control occurs.

Referring back to FIG. 7, the pitch of each rotor blade 214 iscontrolled via a pitch control mechanism 280 through a link 282 that isattached to a control arm 284. The pitch control mechanism 280 can beadjusted mechanically to adjust the pitch angles of all the rotor blades214 simultaneously. In propeller 210 (or a similar propellerapplications) the points at which the support members 222 attach to thecentral hub 212 are selected to allow the rotor blade 214 to deflect orotherwise move to a high pitch angle if the pitch control (which isusually hydraulically driven with oil pressure generated by a pump thatis dependent on engine rotation) is compromised or lost altogether. Byconfiguring the rotor blades 214 and the attachment angle/position ofthe support members in such a way as to increase the pitch thereof inthe event of a loss of control, less drag is experienced on the aircraftand the tendency for causing an overspeed condition is reduced.

Referring specifically to FIGS. 9 and 10, the rotor blade 214 includesthe airfoil portion 232 (only a portion of the full blade is shown) anda hollow root portion 234 with the two support members 222 integrallyformed with or otherwise attached to an outer surface (290 in FIG. 10)of the airfoil portion and extending inward through the hollow rootportion. As can be best seen in FIG. 10, the support members 222 eachextend up a length of the inside surface 290 and attach thereto atpoints substantially distal from the lower end of the rotor blade 214.The specific distances from the lower end of the rotor blade 214 atwhich the support members 222 attach are selected to impart a desirableamount of flexibility to the airfoil portion relative a hub assembly towhich the rotor blade is attached. The control arm 284 extends from theroot portion 234 to provide a point at which the pitch of the rotorblade 214 can be adjusted using the pitch control mechanism. The outershell over the hollow inboard part of the blade is purposely built oftorsionally stiff material(s) such that a torsional pitch control forceapplied to the lever arm at the base will be properly transferred to theouter airfoil such that it responds in unison with the base. As can bebest seen in FIG. 9, a pressure surface 292 of the rotor blade 114 issubstantially uninterrupted to facilitate a less turbulent intake of airby a propeller into which the rotor blade 214 is incorporated.

Referring now to FIGS. 11-13, each of the pins 300 includes twoassociated shells, viz., a first shell 302 and a second shell 304, andtwo wedges, viz., a first wedge 306 and a second wedge 308, receivedbetween the two associated shells. The first shell 302 and the secondshell 304 are each attached to a collar 310 which is integral with athreaded rod 312 and positioned substantially at the center of the rod.Each end of the rod is threaded in opposing directions, i.e. one end hasa right-hand thread and one end has a left-hand thread. The wedges areeach tapered to one respective end thereof such that when the firstwedge 306 is received over the rod 312 from a first end and the secondwedge 308 is received over the rod from a second end such that thetapered portions thereof face each other, turning the rod axially in onedirection (e.g., using a wrench) causes the wedges to translate towardsthe central collar 310. Likewise, turning the rod in the oppositedirection causes the wedges to move apart from the center.

Referring specifically to FIG. 12, upon rotating the rod 312 through thewedges 306 and 308, the wedge on each end of the rod being translatedtoward the collar (arrow A). The taper of the wedges drives the firstshell 302 and the second shell 304 in opposite directions, as indicatedby arrow B and arrow C, thereby allowing the shells to tighten to alesser tolerance. When the rod 312 is turned axially in an opposingdirection, the wedges are translated away from the collar 310, and theywithdraw, thereby allowing the first shell 302 and the second shell 304to relax to a greater tolerance. The optimum adjustment for the pin 300is one in which the tolerances on each end of the pin are the same or atleast within a specified range.

Although this invention has been shown and described with respect to thedetailed embodiments thereof, it will be understood by those of skill inthe art that various changes may be made and equivalents may besubstituted for elements thereof without departing from the scope of theinvention. In addition, modifications may be made to adapt a particularsituation or material to the teachings of the invention withoutdeparting from the essential scope thereof. Therefore, it is intendedthat the invention not be limited to the particular embodimentsdisclosed in the above detailed description, but that the invention willinclude all embodiments falling within the scope of the appended claims.

1. A rotor blade for an aircraft engine, said rotor blade comprising: anairfoil; a first support member flexibly attached to said airfoil; and asecond support member flexibly attached to said airfoil; said firstsupport member and said second support member being attachable to arotatable hub and movable relative to said rotatable hub to allow apitch of said rotor blade to be varied.
 2. The rotor blade of claim 1,wherein said rotor blade further comprises a pivot point about whichsaid rotor blade is pivotal about a rotor blade axis extending axiallythrough said rotor blade.
 3. The rotor blade of claim 2, wherein saidrotor blade is pivotal via independent axial rotation of a first portionof said hub assembly to which said first support member is attachedrelative to a second portion of said hub assembly to which said secondsupport member is attached.
 4. The rotor blade of claim 1, wherein saidairfoil comprises a root through which said first support member andsaid second support member extend, said root being rotatable on said hubvia a bearing.
 5. The rotor blade of claim 1, wherein said first supportmember and said second support member are attachable to said rotatablehub using a preloadable pin.